1. The Field of the Invention
The present invention relates to procedures for using an endodontic instrument to prepare a root canal of a tooth for receiving a sealer or filler material. More particularly, the invention relates to a method of using a super-elastic apical endodontic file either manually or in a reciprocating hand piece.
2. The Relevant Technology
When a root canal of a living tooth becomes infected or abscessed, discomfort and, in many cases, severe pain can result. In the early days of dentistry the only solution was to pull the tooth. More recently, however, dental practitioners have learned to successfully remove the pulp material that forms the nerve of the tooth, which has become infected. After careful preparation of the canal that contained the nerve material the canal is refilled with an inert filling material, such as gutta percha. This process allows the patient to retain the tooth.
To achieve a successful root canal restoration, the dental practitioner must carefully and, as completely as possible, remove the infected pulp material. The removal process typically includes shaping the root canal so that it can be effectively and successfully filled and sealed with an inert material to reduce the possibility of further infection.
Cleaning and shaping the root canal in preparation of receiving a sealing or filling material is achieved by the use of metal files that include cutting surfaces for removing tissue in the root canal. The cutting surfaces are typically formed by helical flutes formed in the file. Some existing endodontic instruments and manufacturing methods are described in U.S. Pat. No. 4,934,934; U.S. Pat. No. 5,653,590; and U.S. Pat. No. 5,762,541.
Since root canals are seldom straight, often having bends and twists, at least some endodontic files are advantageously flexible. Currently preferred materials of construction include stainless steel, and more recently, nickel-titanium (Ni—Ti) alloys.
Endodontic files made from super-elastic materials such as Ni—Ti alloys have been found to be particularly useful for cleaning a root canal because they exhibit good flexibility, resilience and strength, and are not likely to fail during use. Flexibility and strength are important to avoid file breakage during the cleaning process.
As mentioned above, endodontic files typically have a helical or similar cutting edge along the length of the file. An endodontic file is used to remove tissue from the root canal by turning (i.e., twisting) the file within the root canal and/or moving the file up and down in the root canal.
The turning motion of the endodontic file in a root canal can be accomplished by hand or alternatively, by a powered hand piece. Hand manipulated endodontic files have a handle on the end that gives the practitioner the ability to grip and manipulate the file as desired. An endodontic file used in a powered hand piece has a chuck on one end for placing the file in the powered hand piece. The advantage of a powered hand piece is that it can be easier and quicker for a practitioner to use.
One problem with some rotating powered hand pieces is that once the cutting edge catches on the tissue and begins cutting, the cutting edge can sometimes dig in and remove excessive amounts of tissue. To overcome the problem with “digging in,” some powered hand pieces reciprocate. A reciprocating hand piece oscillates back and forth, thereby preventing excessive cutting from the cutting edge digging in.
While a reciprocating hand piece provides a significant advantage for conveniently removing tissue in the root canal, the use of a reciprocating hand piece has been somewhat limited with endodontic files made from super-elastic materials. In particular, apical endodontic files made of super-elastic materials are currently not used in reciprocating hand pieces. On the other hand, using a rigid apical file made from stainless steel with a reciprocating handpiece in inadvisable since the tip of the rigid apical file can bore right into the root canal wall and/or cause what is know as “ledging”.
Apical files are used to clean the apical third of the tooth. Cleaning this portion of the root canal can be more technical because of the narrow spaces in the apex and the delicateness of the apex and apical files. Apical files are more susceptible to breaking and their breakage is more difficult to remedy. Furthermore because apical files are long and thin, they are more flexible than files used to clean other portions of the root canal. The flexibility of apical files made from super-elastic materials is such that the files have a tendency to simply wind and unwind as they are reciprocated in a reciprocating hand-piece. Winding and unwinding decreases the cutting effect of the reciprocating file and increases the risk that the apical file will break. Consequently, apical endodontic files made from super-elastic materials such as NiTi are only used in a powered hand piece that rotates in only one direction.
Therefore, what is needed is a method of using an apical file made from a super-elastic material either manually or with a powered hand piece that minimizes the effects of winding and unwinding and reduces the risk that the apical file will break during use in the apex.